The salivary glands synthesize and secrete a number of proteins having diverse biological functions. Such proteins facilitate lubrication of the oral cavity (e.g., mucins and proline-rich proteins), remineralization (e.g., statherin and ionic proline-rich proteins) and digestion (e.g., amylase, lipase and proteases) and provide anti-microbial (e.g., proline-rich proteins, lysozyme, histatins and lactoperoxidase) and mucosal integrity maintenance (e.g., mucins) capabilities. In addition, saliva is a rich source of growth factors synthesized by the salivary glands. For example, saliva is known to contain epidermal growth factor (EGF), nerve growth factor (NGF), transforming growth factor-alpha (TGF-.alpha.), transforming growth factor-beta (TGF-.beta.), insulin, insulin-like growth factors I and II (IGF-I and IGF-II) and fibroblast growth factor (FGF). See, for example, Zelles et al., J. Dental. Res. 74(12): 1826-32, 1995. Synthesis of growth factors by the salivary gland is believed to be androgen-dependent and to be necessary for the health of the oral cavity and gastrointestinal tract.
Some salivary gland-produced proteins, such as EGF, are believed to have systemic wound healing effects. Effective wound healing appears to require extended exposure of afflicted tissue to growth factors, which may be facilitated in the oral cavity and gastrointestinal tract by mucin at the epithelial/environmental interface acting to capture saliva growth factors. Also, combinations of growth factors, such as those found in saliva, may be necessary for optimal wound healing. Moreover, protease inhibitors, which are also produced by the salivary glands, appear to facilitate growth factor activity.
In addition, saliva contains adhesive proteins having protective properties with regard to infection by exogenous microorganisms. Such adhesive proteins bind exogenous microorganisms and facilitate the degradation or expulsion thereof. From this rich source of biologically relevant proteins, new secreted proteins are sought. Also, given the importance and variety of saliva proteins, conditions involving inadequate saliva production or secretion have inspired investigative effort.
Rattus norvegicus common salivary protein 1 (U00964.sub.-- 1) and a murine homolog of common salivary protein 1 (S76879.sub.-- 1) have been discovered and characterized. See, for example, Girard et al., J. Biol. Chem. 268(35): 26592-601, 1993. Common salivary protein 1 is so designated as a result of the expression thereof in cells of all major salivary glands. Evidence exists that such expression is androgen-regulated in the rat submandibular gland. Common salivary protein 1 does not include structural features associated with many other salivary proteins, including tandemly repeated sequences, a high density of charged residues and/or an unusually large proportion of a few amino acids. Common salivary protein 1 is somewhat homologous to spermine binding proteins discussed below, but lacks the highly acidic carboxy terminal domain thereof. Thus, the proteins may be evolutionarily related without being functionally related.
Salivary glands share significant features with other glands, such as the prostate gland. For example, the salivary glands and prostate gland are classified as slow replicators with respect to their proliferative capacity. See, for example, Zajicek, Med. Hypotheses 7(10): 1241-51, 1981. Such slow replicators exhibit similar onotgenies and proceed during regeneration and neoplasia through similar stages. The prostate gland also appears to produce growth factors, such as EGF and NGF, and other biologically important proteins, such as kallikreins. See, for example, Hiramatsu et al., Biochem. Int. 17 (2): 311-7, 1988, Harper et al., J. Biol. Chem. 257(14): 8541-8, 1982 and Brady et al., Biochemistry 28(12): 5203-10, 1988. Prostate gland function also appears to be androgen-dependent. Consequently, proteins associated with the prostate gland are also sought.
Glandular function is believed to be androgen-dependent. Expression of secreted glycoproteins, having spermine-binding activity, by mouse and rat prostate has also been postulated to be androgen-dependent. See, for example, Mills et al., Nucleic Acids Res. 15: 7709-24, 1987. Spermine-binding protein mRNA expression appears to be induced by exposure to androgens, with an increase therein by 2-3 fold being observed within 16 hours and continuing for several days. Thus, intracellular levels of specific hormone-dependent mRNA, such as spermine binding protein mRNA, are useful markers of hormone action. See, Labrie et al. , Endocrinology 124(6): 2745-54, 1989. Spermine-binding protein is also useful for studying cAMP-independent protein kinases, because the protein is under androgenic control through the action of such kinases. See, for example, Goueli et al., Biochem. J. (England) 230(2): 293-302, 1985.
Spermine-binding proteins bind to polyamines, such as spermine. Prostatic fluid, for example, is rich in polyamines, and spermine-binding proteins have therefore been postulated to serve as carriers of such polyamines in the seminal fluid. Spermine-binding proteins may also be useful to disrupt spermine-mediated pig lens soluble protein aggregation to form cataracts. See, for example, Maekawa, Mie. Med. J. 39(2): 221-8, 1989. In addition, spermine binds to and is believed to modulate the activity of the N-methyl-D-aspartate (NMDA) receptor, a ligand-gated ion channel (Bergeron et al., J. Med. Chem. 38: 425-8, 1995). Also, spermine is believed to effect vascular smooth muscle cell contractility via inhibition of myosin phosphatase (Sward et al., Am. J. Physiology 269(3 pt. 1): C563-71, 1995). Thus, homologs of spermine-binding proteins are sought.
The present invention provides such polypeptides for these and other uses that should be apparent to those skilled in the art from the teachings herein.